Process of treating crude benzene hexachloride to derive therefrom a product having enhanced gamma isomer content



United States Patent M 2,718,531 PROCESS OF TREATING CRUDE BENZENE HEXA- CHLORIDE TO DERIVE THEREFROM A PROD- UCT HAVING ENHANCED GAMMA ISOMER CONTENT No Drawing. Application January 29, 1952, Serial No. 268,936

Claims. (Cl. 260-648) Our invention relates to a process of making benzene hexachloride containing an enhanced proportion of gamma isomer from crude benzene hexachloride obtained by the addition chlorination of benzene.

As so produced, crude benzene hexachloride consists of several isomers of which only the gamma isomer has insecticidal values. Commonly the crude product contains only 14-15% of the gamma isomer. The other isomers amounting to 84-85% are unnecessary for insecticidal purposes. Hence it is desirable for many purposes to furnish a product which is richer in the gamma isomer or may even consist of substantially 100% gamma. Since the various isomers have different solubilities in different solvents, many proposals for making a benzene hexachloride product having enhanced gamma content have sought to take advantage of this difference in solubility.

Since the unwanted alpha and beta isomers are more soluble in the hot, most prior proposals have sought to extract the crude benzene hexachloride in the cold; however cold extraction is slow and inefiicient, especially so in the case of crude benzene hexachloride which as obtained by crystallization from, or evaporation of, henzene solutions is in the form of a crystalline or lumpy mass which in the absence of thorough grinding is difficult to penetrate by cold solvents.

It is therefore a principal object of our invention to devise an improved process of benzene hexachloride manufacture in which the crude benzene hexachloride is attacked by a solvent in the hot, breaking up its crystalline structure or agglomerates and rendering unnecessary a preliminary grinding operation. In so doing, insuificient solvent is used. to dissolve substantially all of the gamma isomer (and hence substantial quantities of the alpha and beta isomers), leaving the remaining gamma for subsequent extractions which, because of the more favorable condition of the material, may if desired be carried out either at a lower or preferably at boiling temperatures followed by cooling of the extraction mixture.

A still further object is to permit the use of a solvent for the hot extraction which is already saturated with respect to the alpha and beta isomers but which has substantial capacity for dissolving the gamma isomer.

A still further object is to permit the use of a substantial excess of hot solvent to further break up the crystalline structure of the mass and then at the termination of the refluxing operation boil off such excess. Alternatively instead of boiling off the excess, the solution may be separated from the residue and then contacted with fresh crude benzene hexachloride.

Other objects of our invention and the advantages thereof will be apparent as the description proceeds and the novel features of the invention will be pointed out in the appended claims.

While many solvents have been proposed for the carrying out of a process for making benzene hexachloride having an enhanced proportion of the gamma isomer,

Patented Sept. 20, 1955 we prefer the use of a solvent which in addition to having a preferential solubility as respects the gamma isomer, answers certain further requirements, i. e., it should have at least moderate dissolving power for the gamma isomer as otherwise excessively large quantities of solvent would have to be handled per pound of high gamma product obtained. On the other hand, if the solvent has too great a dissolving power, the solutions obtained have insulficient volume to provide easy separation from the residues that do not dissolve. Again the solvent should not be unduly toxic. It further should not be too highly volatile, nor, since large volumes have to be distilled, should it have too high a boiling point or too high a latent heat of vaporization. From a study of these and other factors, we have been led to choose as our preferred so1 vents those from the group of compounds consisting of the oxy-derivatives of the saturated lower aliphatic radicals represented by the alcohols and ethers, especially those which have a boiling point range of from 54 C. to C. Examples of such solvents preferred by us are as follows:

Alcohols: Boiling point, C.

Ethyl-n-propyl ether 62-63 Ethyl-isopropyl ether 54 Ethyl-n-butyl ether 91.4 Ethyl-isobutyl ether 78-80 Ethyl-tert-butyl ether 70 As will be evident from the specific examples which follow, our improved process lends itself to the use of an efiicient system of having the solvent flow countercurrent to the movement of the solid benzene hexachloride, such that fresh solvent will always be used as a Washing or extracting agent on the exhausted nearly gamma-free benzene hexachloride, whereas fresh benzene hexachloride will meet first a solution containing some gamma isomer more or less saturated with the alpha isomer. Thus several extraction steps may be employed and the hot solution upon moving from one extraction operation to the next becomes richer and richer in gamma isomer but in spite of the elevated temperature can dissolve but little of the alpha because it is already saturated or substantially saturated therewith. The number of extraction steps may be varied as desired with the limit thus far found to be practicable of four or five. To some extent the same effect may be had by carrying out the whole extraction in a single vessel but using a greatly increased amount of crude benzene hexachloride relative to the amount of the solvent.

It will be further noted in general that the cooling operations are kept at a minimum both in number and in the amount of cooling. In general it is necessary to cool the materials in the extraction vessel in order to stop the refluxing action and facilitate a separation of the solution from the undissolved residue whether by decantetion or filtration. Where filtration is employed, it is usually necessary to employ a somewhat lower temperature than when the solution is decanted. However, cooling has the advantage that more of the alpha and beta isomers are dropped out, thereby increasing the percentage in the solution of the gamma isomer. The foregoingremarks apply particularly to the first extraction wherein which preferably is maintained at the boiling temperature. In the second and subsequent extractions, the temperature may either be maintained somewhat lower (since the physical structure of the benzene hexachloride is now such as will facilitate contact of the comparatively fresh solvent) or the temperature may be as high as the boiling point of the solvent followed by cooling of the mixture before separation of the solution.

Various ways of recovering the high gamma benzene hexachloride from the solution may be had. Preferably such solution is concentrated by boiling oil a quantity of the pure solvent-the amount of solvent removed may vary from about 20 to about 75% with preference given to the range from 50 to 75%. Thus if as little as 20% of the solvent is distilled off from the extract, cooling and crystallization will yield a small crop of crystals with a gamma content of more than 90% but not the pure gamma isomer. However, by distilling off a much larger proportion of the solvent, a crystalline material is obtained with a gamma content of 60-75% which is directly usable for many insecticidal purposes. If desired, this product may be redissolved in methanol or other solvent and recrystallized to yield the pure gamma isomer known as lindane.

It will be understood that if the richest extract were to be evaporated to dryness, such a product would contain practically all the gamma isomer originally present in the crude benzene hexachloride. However, the presence of the delta isomer and other impurities would cause the product to have a sticky, semi-solid consistency and an unpleasant odor and hence be undesirable for many purposes.

Reference has already been made to extracting the crude benzene hexachloride in the hot and the consequent breaking up of the physical structure of the crude material. Technical benzene hexachloride is usually obtained by adding chlorine to benzene under irradiation and leaving a substantial portion of the benzene unreacted. Then the mixture is subjected to distillation to drive off the unreacted benzene, leaving the benzene hexachloride in molten form to be solidified on a so-called flaking roll. The crude benzene hexachloride so obtained is in lumps or flakes which do not readily fall apart by treatment with a solvent in the cold. To obviate this drawback, it has been proposed to subject the crude benzene hexachloride to a preliminary grinding operation which, however, is diflicult to carry out because of the tendency of the particles to soften and to agglomerate. However in our improved process the hot solvent has the ability to rapidly penetrate to the interior of flakes and lumps of the crude material and leach out the locked up gamma isomer, whereby grinding is rendered unnecessary and a quick and sharp separation of the solvent from the solid residue results, thereby making it possible for the most part to employ simple decantation instead of filtration. If desired, the crude molten benzene hexachloride may be added directly to the solvent wherein it quickly disintegrates.

The mother liquor from the product of the various examples given, in which has accumulated the various im purities of the system, including large quantities of the delta isomer, still contains a substantial quantity of the valuable gamma isomer. It may be processed in known manner for the recovery of further quantities thereof.

Our invention will be best understoodby reference to the following illustrative examples, of which Examples 1-5 show various ways of treating the hot solution from the extraction of the fresh crude benzene hexachloride to obtain a concentrate rich in the gamma isomer, whereas Examples 6-10 show the use of solvents other than methanol.

Example 1 1500 parts of crude benzene hexachloride containing 14.7% of the gamma isomer were agitated and heated decantation to be practicable.

for 15 minutes at reflux, i. e., boiling temperature, with 2000 parts of methanol extract obtained in the preceding of a series of extractors where partly extracted benzene hexachloride was washed with once spent methanol solution containing 1750 parts of methanol and 250 parts of benzene hexachloride by weight. Heating and agitating was then discontinued and the supernatant hot liquid was decanted from the settled residue.

The residue was washed free from gamma isomer with hot methanol. The washing liquid which was saturated with the alpha isomer was used for heating more crude benzene hexachloride at reflux temperature as described.

The solution decanted in the first step, saturated in regard to the alpha, but not yet in regard to the gamma isomer, was once more mixed with 1500 parts of crude benzene hexachloride and heated for 15 minutes at reflux temperature. Agitating and heating was discontinued and the extract filtered from the settled residue and transferred to a still where 75 of the solvent was distilled oil. The concentrated extract was then rapidly agitated and cooled to 5 C. The precipitated crystalline material was filtered and dried. Thus 500 parts of a product with 71% of gamma isomer was obtained.

Example 2 2000 parts of crude benzene hexachloride containing 14.7% of the gamma isomer were agitated with 3500 parts of a hot methanol solution saturated with pre dominantly the alpha isomer and heated at reflux temperature and agitation for 15 minutes. That solution contained approximately 22.5% of benzene hexachloride. Heating and agitating was then discontinued; the super-. natant liquid was decanted from the settled residue.

The residue was further extracted with 2500 parts of fresh methanol at C. and filtered at room temperature. It was then practically free from gamma isomer, that is, after drying it contained only 0.3% of gamma isomer. The filtrate which was saturated with the alpha isomer was the solution to be used for treating fresh benzene hexachloride as described.

The solution decanted in the first step was charged to a still where 70% of the solvent was evaporated off.

The concentrated extract, left in the still, was transferred to a crystallizer where under cooling and agitation a product was precipitated which on filtering and drying yielded 360 parts of a high gamma concentrate with of gamma isomer.

Example 3 2000 parts of crude benzene hexachloride containing 14.7% of the gamma isomer were mixed with a solution containing 950 parts of methanol and 250 parts of benzene hexachloride isomers and heated under reflux and agitation for one hour.

The mixture was then cooled down to room temperature and filtered since insufficient liquid was present for The residue from the above extraction was further extracted in the hot, i. e., at approximately 67 C. with 2500 parts of a solution of benzene hexachloride isomers in methanol obtained as washing liquid in a previous extraction.

After distilling otf approximately 1500 parts of methanol, the mixture was cooled to room temperature and filtered. The filtrate, amounting to 1200 parts, containing approximately 950 parts of methanol, was used for treating 2000 parts of fresh benzene hexachloride as described. The residue was washed finally with 2600 parts of fresh methanol and the washing liquid was used in the second extraction step as described. The dried residue, largely consisting of the alpha isomer, had a gamma isomer content of 0.3%.

The solution obtained in the first extraction step was put to a still where 60% of the solvent was recovered.

The thus concentrated extract was rapidly cooled under agitation and yielded a crop of crystalline material, which after filtration and drying, resulted in a product containing 75% of the gamma isomer.

Example 4 1500 parts of crude benzene hexachloride containing 14.5% gamma isomer was refluxed for 30 minutes with 1000 parts of a methanol extract containing 740 parts of methanol and 260 parts of benzene hexachloride isomers. Heating was then discontinued and the mixture was cooled to 35 under agitation and filtered. The filtrate was transferred to a still.

The undissolved portion (residue #1) from the above treatment was heated with 2600 parts of previously obtained washing liquid at 50 C. Agitation was then discontinued. The supernatant liquid was decanted (leaving residue #2), and approximately two-thirds of this extract was used for treating (refluxing) crude benzene hexachloride as described. The remainder was put to the still and there combined with the extract obtained from the treatment (refluxing) of crude benzene hexachloride in the first step.

Residue #2 (containing undecanted solution) was washed with 1200 parts of fresh methanol at 50 C. and filtered. The filtrate was reserved for the next operation of washing residue #1.

The combined extracts were concentrated in a still by removal of 50% of the solvent by volume. The concentrated extract, crystallized under cooling an agitation, yielded 290 parts of a material containing 60% of the gamma isomer.

Example 5 Three extraction steps were used. 2000 parts of crude benzene hexachloride containing 14.3% if the gamma isomer was charged to extractor #1 and mixed with 2800 parts of methanol extract obtained during the previous cycle by further leaching the partly extracted benzene hexachloride in the two subsequent extractions of the series. The mixture in extractor #1 was then heated and agitated under reflux for 15 minutes, after which the solvent was allowed to distill over and when 400 parts distillate was collected, heating was discontinued and cooled to 50 C. Agitation was now shut ofl and undissolved solids allowed to settle for 30 minutes. Then 1360 parts of the supernatant liquid was siphoned ofl and charged directly to a still where 490 parts of solvent was distilled off (leaving residue #1). The residual concentrated extract was rapidly cooled at 5 C. under agitation and the precipitated crystals filtered and dried. Thus, 390 parts of a product with 68% of gamma isomer was obtained. The once extracted benzene hexachloride was left in the same extractor and there treated for one hour under reflux and agitation with 1760 parts of methanol washing liquid obtained in the third subsequent extraction step during the previous cycle. After cooling to 40 C., and settling, 1600 parts of the supernatant liquid was decanted (leaving residue #2), and this liquid reserved for treating a fresh batch of crude benzene hexachloride in the next cycle.

The residue #2 in the extractor was then mixed with 1360 parts of fresh methanol and treated for a third time at reflux temperature, then cooled to 40 C. and filtered. The filter cake (residue #3) was washed with 400 parts of fresh methanol, resulting in a total of 2960 parts of filtrate which was reused as makeup and washing liquid in the subsequent cycle.

The gradual progress in the three step series-extraction is shown in the following table:

Gamma content, percent Example 6 2000 parts of crude benzene hexachloride containing 14.7% of the gamma isomer were agitated and heated for 30 minutes at reflux temperature with 4000 parts of industrial ethyl alcohol which had been used in a previous step as washing liquid on partly extracted benzene hexachloride. Heating and agitating was then discontinued and the supernatant liquid was decanted from the settled residue and the latter washed with hot ethyl alcohol. The washing liquid thus obtained was saturated with the alpha isomer and used for heating and extracting crude benzene hexachloride as described.

The solution obtained in that first step was decanted from the settled residue and transferred to a still where 75% of the solvent was distilled off. The remaining concentrated extract was rapidly cooled under agitation and the crop of crystals filtered and dried. The yield was 350 parts of a high gamma product with 63% of gamma isomer.

Example 7 2000 parts of crude benzene hexachloride with 14.5% of gamma isomer were heated for 15 minutes under reflux and agitation with 5000 parts of an isopropyl alcohol solution saturated with the alpha isomer. Heating was then discontinued and the supernatant solution removed from the residual solids.

The residue was further extracted with 3000 parts of isopropyl alcohol and filtered. The filtrate which was saturated with the alpha isomer was the liquid to be used on fresh benzene hexachloride as described.

The concentrated extract of the crude benzene hexachloride was evaporated to one-fourth of its volume and the concentrated extract transferred to a crystallization vessel. There, under cooling and agitation, a precipitate was obtained which on filtering and drying yielded 340 parts of a product containing 62.5% of gamma isomer.

Example 8 600 parts of crude benzene hexachloride containing 14.5 of gamma isomer were dissolved in 2800 parts of isopropyl alcohol under reflux and agitation.

Heating was then discontinued and the hot supernatant solution decanted from the crystallized material. Onehalf of the decanted extract was once more contacted with 600 parts of crude benzene hexachloride under reflux and agitation. The solution thus obtained was combined with the other portion of the previously obtained extract and transferred to a still where 75% of the solvent was evaporated oif. The concentrated extract was caused to deposit crystals by rapid cooling under agitation. 220 parts of a product was obtained on filtration and drying which contained 63% of the gamma isomer.

Example 9 2000 parts of crude benzene hexachloride containing 14.5 of the gamma isomer were heated under reflux and agitation for 15 minutes with 2700 parts of normal propyl alcohol previously used for washing partly extracted benzene hexachloride. Agitating and heating was then discontinued and the solution separated from the solid residue.

The solution was charged to a still and concentrated to one-fourth of its volume. The concentrated extract was cooled under agitation whereby a crystalline precipitate was obtained, which after filtration and drying yielded 380 parts of a product of 61% of gamma isomer. The residue from the first extraction step was further extracted with 2500 parts of normal propyl alcohol and the washing liquid thus obtained was saturated with the alpha isomer and used on fresh benzene hexachloride as described.

Example 10 1500 parts of crude benzene hexachloride with 14.5 of gamma isomer were heated for 10 minutes under reflux and agitation with 2500 parts of isopropyl ether saturated with the alpha isomer. Agitating and heating was then discontinued and the solution decanted from the solid residue. The solution was charged to a still where 70% of the solvent was evaporated off.

The concentrated extract was cooled under agitation. The crystalline precipitate was filtered and dried and yielded 300 parts of a product with 60% of the gamma isomer. The residue from the first extraction step was washed with 2300 parts of fresh isopropyl ether. The washing liquid was saturated with the alpha isomer and used on fresh benzene hexachloride as described.

Example 11 1500 parts of benzene hexachloride with 14.5% of the gamma isomer, extracted with methanol as described in Example 2, yielded 280 parts of a high gamma concentrate with 65% of gamma isomer. The mother liquor remaining from crystallization was evaporated to dryness and resulted in 234 parts of a gummy, semi-solid residue, largely consisting of the delta isomer and impurities, but still containing 14% of the gamma isomer.

The residue was poured into 75 parts of isopropyl alcohol and the mixture agitated and cooled to C. The precipitate was then filtered and dried and yielded 132 parts of a crystalline material which contained 19.6% of the gamma isomer.

We claim:

1. In the manufacture from crude benzene hexachloride obtained by the addition chlorination of benzene, of a benzene hexachloride containing an enhanced proportion of the gamma isomer by the action on said crude benzene hexachloride of a solvent in which the gamma isomer is more soluble than the alpha and beta isomers, the cyclic method which comprises extracting said crude benzene hexachloride by refluxing a mass of same with a solvent selected from the group of compounds consisting of lower saturated aliphatic alcohols and lower saturated aliphatic ethers and having a boiling point not substantially less than 54 and not substantially more than 120 C., said solvent prior to contact with said crude benzene hexachloride being already substantially saturated with the alpha isomer but still having substantial capacity for dissolving the gamma isomer, thereby breaking up the physical structure of said mass and facilitating the action of a subsequent solvent thereon, cooling the mixture of solvent and undissolved residue sufficiently to stop refluxing and to facilitate separation of the solvent, said solvent when separated from said mass being insufficient in amount to dissolve substantially all of the gamma isomer, separating the solution from the undissolved residue, concentrating said solution and causing the more concentrated solution to deposit crystals rich in the gamma isomer, extracting said undissolved residue with a relatively fresh portion of said solvent and then utilizing the so enriched solvent to extract a fresh portion of crude benzene hexachloride.

2. In the manufacture from crude benzene hexachloride obtained by the addition chlorination of benzene, of a benzene hexachloride containing an enhanced proportion of the gamma isomer by the action on said crude benzene hexachloride of a solvent in which the gamma isomer is more soluble than the alpha and beta isomers, the cyclic method which comprises extracting said crude benzene hexachloride with a solvent at a temperature which approximates the boiling point thereof, said solvent being selected from the group of compounds consisting of lower saturated aliphatic alcohols and lower saturated aliphatic ethers and having a boiling point not substantially less than 54 and not substantially more than 120 C., said solvent prior to contact with said crude benzene hexachloride being already substantially saturated with the alpha isomer but still having substantial capacity for dissolving the gamma isomer, thereby breaking up the physical structure of said mass and facilitating the action of a subsequent solvent thereon, cooling the mixture of solvent and undissolved residue sufficiently to facilitate separation of the solvent, said solvent when separated from said mass being insuflicient in amount to dissolve substantially all of the gamma isomer, separating the solution from the undissolved residue, concentrating said solution so as to leave a substantial portion unevaporated of the liquid component started with and causing the concentrated solution to deposit crystals rich in the gamma isomer, extracting said undissolved residue with a relatively fresh portion of said solvent and then utilizing the so enriched solvent to extract a fresh portion of crude benzene hexachloride.

3. The method according to claim 2 in which methanol is the solvent and the mixture of solvent and residue is cooled to within the range of to 40 C.

4. The method according to claim 2 in which an excess of solvent is used in the extraction first mentioned and in Which such excess is boiled off prior to the separation of the solvent from the residue.

5. The method according to claim 2 in which an excess of solvent is used in the extraction first mentioned and then after separation of the solvent from the undissolved residue such solvent is contacted with a further quantity of crude benzene hexachloride.

6. The method according to claim 5 in which the second extraction is carried out at a temperature substantially below the boiling point of the solvent.

7. The method according to claim 2 in which the solvent is methanol.

8. The method according to claim 2 in which the solvent is a propanol.

9. The method according to claim 2 in which the solvent is a propyl ether.

10. The method according to claim 2 in which the solvent is a mixed ether containing two different lower aliphatic radicals.

References Cited in the file of this patent UNITED STATES PATENTS 2,486,688 Thomas et al Nov. 1, 1949 2,585,898 Kauer Feb. 12, 1952 FOREIGN PATENTS 491,132 Belgium Mar. 16, 1950 

2. IN THE MANUFACTURE FROM CRUDE BENZENE HEXACHLORIDE OBTAINED BY THE ADDITION CHLORINATION OF BENZENE, OF A BENZENE HEXACHLORIDE CONTAINING AN ENHANCED PROPOR-P TION OF THE GAMMA ISOMER BY THE ACTION ON SAID CRUDE BENZENE HEXACHLORIDE OF A SOLVENT IN WHICH THE GAMMA ISOMER IS MORE SOLUBLE THAN THE ALPHA AND BETA ISOMERS, THE CYCLIC METHOD WHICH COMPRISES EXTRACTING SAID CRUDE BENZENE HEXACHLORIDE WITH A SOLVENT AT A TEMPERATURE WHICH APPROXIMATES THE BOILING POINT THEREOF, SAID SOLVENT BEING SELECTED FROM THE GROUP OF COMPOUNDS CONSISTING OF LOWER SATURATED ALIPHATIC ALCOHOLS AND LOWER SATURATED ALIPHATIC ETHERS AND HAVING A BOILING POINT NOT SUBSTANTIALLY LESS THAN 54* AND NOT SUBSTANTIALLY MORE THEN 120* C., SAID SOLVENT PRIOR TO CONTACT WITH SAID CRUDE BENZENE HEXACHLORIDE BEING ALREADY SUBSTANTIALLY SATURATED WITH THE ALPHA ISOMER BUT STILL HAVING STUBATNTIAL CAPACITY FOR DISSOLVING THE GAMMA ISOMER, THEREBY BREAKING UP THE PHYSICAL STRUCTURE OF SAID MASS AND FACILITATING THE ACTION OF A SUBSEQUENT SOLVENT THEREON, COOLING THE MIXTURE OF SOLVENT AND UNDISSOLVED RESIDUE SUFFICIENTLY TO FACILITATE SEPARATION OF THE SOLVENT, SAID SOLVENT WHEN SEPARATED FROM SAID MASS BEING INSUFFICIENT IN AMOUNT TO DISSOLVE SUBSTANTIALLY ALL OF THE GAMMA ISOMER, SEPARATING THE SOLUTION FROM THE UNDISSOLVED RESIDUE, CONCENTRATING SAID SOLUTION SO AS TO LEAVE A SUBSTANTIAL PORTION UNEVAPORATED OF THE LIQUID COMPONENT STARTED WITH AND CAUSING THE CONCENTRATED SOLUTION TO DEPOSIT CRYSTALS RICH IN THE GAMMA ISOMER, EXTRACTING SAID UNDISSOLVED RESIDUE WITH A RELATIVELY FRESH PORTION OF SAID SOLVENT AND THEN UTILIZING THE SO ENRICHED SOLVENT TO EXTRACT A FRESH PORTION OF CRUDE BENZENE HEXACHLORIDE. 